I rarely use dye at all for any one of the numerous neagtive reasons posted here and on other forums, but be it flesh side or grain side you must allow the dye time enough to level out and dry completely ( depending on humidity conditions this could take up to 24 hours) Then buff with a paper towel several times until the residue coming off is practically none, and then apply Feibing's TanKote to seal. This is about a 99% cure for dyes rubbing off after the treatment. Most people, myself included, tend to rush and try to finish before the dye is bone dry.
Paul